Cameras with auto-focus use a highly-structured object (or target) in the scene being photographed for the auto-focus operations. The position of the focus lens (or focal length) is adjusted to maximize contrast of the target, which indicates that the object is in focus. Although a skilled photographer may understand this concept and ensure that a suitable target is positioned in the focus zone for focusing the camera, the typical camera user simply wants to “point-and-shoot” to take photos.
In point-and-shoot photography, there may not be any suitable targets in the focus zone, resulting in a poorly focused photo. Some cameras use multiple, fixed focus zones to increase the probability of a suitable target being in at least one of the focus zones. However, there still may not be any suitable targets in any of the fixed focus zones, or there may be better targets that are not in any of the fixed focus zones.
Other options are also available, such as using range finders (non-TTL focus modules) to focus the camera lens. However, range finders provide limited control over the focus region, require calibration to match the lens, and increase the cost of the camera. Accordingly, the use of range finders is not practical or cost-effective for most consumer cameras.